The invention herein described relates to a microorganism and the use of this non-obligate bacterial predator of bacteria for the control of bacterial and fungal plant diseases. In particular, it is concerned with the use of a newly-isolated, highly-competitive, gram negative bacterial predator species for such control. Both the cells of this bacterium and the antimicrobial compounds that it produces are involved in the described biological control system.
By way of background, the use of living microbial cells to fight plant disease has received considerable attention in recent years [Lukezic, F. L., et al., in New Directions in Biological Control: Alternatives for Suppressing Agricultural Pests and Diseases, Alan R. Liss, Inc., New York (1990)]. However, the use of non-obligate bacterial predators of bacteria or fungi [Casida, L. E., Jr., Microb. Ecol. 15:1-8 (1988)] has not previously been considered in this context. The non-obligate bacterial predators live in soil. They use soluble nutrients in the environment, but if these are not available, they feed by attacking various other bacteria or fungi in the vicinity. Some of these predators can attack other bacterial predators, which means that interlocking food chains are created. Some, but not all, of these predators have distinct requirements for small amounts of certain metals. They use these metals to aid in breaking dormancy so they can initiate growth. The metals are not needed, however, for the ensuing growth. When these metals are poorly available in the environment, the predators elaborate specific peptide compounds that scavenge and sequester the metals so they will be available. Magnesium and copper are examples of these metals. The grams negative bacterial predators that need copper are resistant to copper and produce a peptide copper growth initiation factor (Cu-GIF) to obtain it. An example is Cupriavidus necator [Makkar, N. S., et al., Int. J. Syst. Bactieriol. 37:323-326 (1987)]. Bacteria like this seem to be at the top of the predatory hierarchy. Their predatory activity is helped by the fact that the Cu-GIF compound itself is quite toxic to other organisms. Therefore, when the predator cell attaches to a prey cell it can deliver a lethal dose of sequestered copper to aid in killing the prey cell.
An object of this invention is to isolate and develop a biologically pure, naturally-occurring microorganism capable of being used for the biological control of fungal and bacterial plant diseases.
It is also an object of this invention to develop materials and methods for the growth of said biological control microorganism and application to plants afflicted with bacterial and fungal diseases.
It is a further object of the invention to develop methods for the control of bacterial and fungal plant diseases using a naturally-occurring microorganism. These and other objects and advantages of the invention will become readily apparent from the following description and are particularly delineated in the appended claims.